The functional state of suppressor lymphocytes will be determined in patients with multiple sclerosis and myasthenia gravis. This will be done by a) evaluating the cytotoxic activity of alloantigen stimulated lymphocytes, b) measuring the amount of immunoglobulin synthesized by pokeweed mitogen stimulated cells and c) determining the capacity of patients' lymphocytes to become suppressor cells upon exposure to extracts of multiple sclerosis brain, myasthenic thymus gland and Concanavalin A. The finding of abnormal suppressor lymphocyte activity in multiple sclerosis and/or myasthenia gravis would provide support for the hypothesis that these diseases result from autoimmune phenomena.